Children in this study were participants in the Childhood Arthritis Prospective Study (CAPS), an ongoing prospective longitudinal inception cohort study which aims to follow children presenting with new onset inflammatory arthritis for a minimum of 5 yrs. The overall aim of this study is to identify genetic and environmental predictors of short- and long-term outcomes of inflammatory arthritis (including response to treatment) in children and to identify the relative contributions of socio-demographic, clinical, psychological, laboratory and genetic factors and treatment in explaining outcome. The study was launched in September 2001 and aims to recruit 1100 children from five tertiary referral centres in England and Scotland: Royal Liverpool Children's Hospital, Liverpool; Booth Hall Children's Hospital, Manchester; Royal Victoria Infirmary, Newcastle; Royal Hospital for Sick Children, Glasgow; and Great Ormond Street Hospital, London. All children aged ≤16 yrs either presenting to the PRh outpatient clinic or admitted as inpatients, with newly diagnosed inflammatory arthritis in one or more joints, which had persisted, according to parent/child history for at least 2 weeks, are invited to participate. Exclusion criteria are septic arthritis, haemarthrosis, arthritis caused by malignancy or trauma, connective tissue disorders such as SLE, MCTD or dermatomyositis. The initial invitation was made by the paediatric rheumatologist and followed-up by the research nurse after the parent had had time to read the study information sheet.
CAPS was approved by the UK multicentre research ethics committee. Written informed consent was obtained from the parent(s)/guardian for all participant children according to the Declaration of Helsinki [6 (link)], and children, if considered able, were asked to provide assent.